Besides light hydrocarbons, some coke is produced and deposited on the catalyst during the catalytic cracking process of inferior hydrocarbon oils due to a condensation reaction, resulting in a decrease of the catalyst activity and selectivity. The properties of the deactivated catalyst can be restored by a high temperature oxidation to burn off the coke on the catalyst, and this process is called as catalyst regeneration. Generally, the catalyst with a carbonaceous hydrocarbon or coke deposited thereon is called as the spent catalyst, and the oxidatively regenerated catalyst is called as the regenerated catalyst. In the early catalyst regeneration method, the oxygen-containing gas was passed through a low velocity fluidized bed and a single stage regeneration method was employed. However, employing such a low gas velocity and gas-solid backmixing fluidized bed regenerator, results in a low gas-solid contact efficiency, a low regeneration speed, a large inventory, a low catalyst regeneration efficiency, an coke content on the regenerated catalyst of about 0.2% by weight, a low coke burning severity of about 100 kg/(h·T) (kg for kilograms of coke burned, h for hour, T for ton of catalyst inventory in the regenerator). With the wide use of zeolite catalyst in the fluid catalytic cracking unit (FCCU), especially USY type zeolite catalyst, the residue coke content on the regenerated catalyst and the regeneration process have a great influence on restoration of the catalyst activity and selectivity. Therefore, the regeneration technology development trend is to reduce the catalyst inventory and improve the catalyst regeneration efficiency. During the FCCU running, both the exposure of the catalyst to high temperature and steam (water vapor) and the deposition of the heavy metals contained in the feedstock on the catalyst surface cause a continuous decrease of the catalyst activity. In order to maintain the equilibrium catalyst activity, additional fresh catalyst (i.e., make-up catalyst) must be added into the reaction-regeneration system. At a constant supplement of the fresh catalyst, the lower the catalyst inventory in the reaction-regeneration system, the higher the catalyst makeup rate and the equilibrium catalyst activity.
U.S. Pat. No. 3,563,911 discloses a two stages catalyst regeneration process, wherein spent catalyst is sequentially introduced to the first dense bed and second dense bed, and contacted with oxygen-containing gas stream to remove coke on the catalyst by a combustion reaction. Resulted flue gases are combined together and carry the entrained catalyst into a dilute settling section. In the first fluidized dense bed the regeneration temperatures is more than 1050° F. (about 565.5° C.). In the second fluidized dense bed the gas superficial velocity is maintained in the range of 1.25 to 6 feet per second (about 0.381 to 1.83 meter per second), and the regeneration temperature is maintained in the range from 1125 to 1350° F. (about 607.2 to 732.2° C.). Compared with a single stage regeneration process, the catalyst inventory in the regenerator is decreased by about 40%, and the coke content is below 0.1 wt % when a low coke burning rate is employed in the regeneration process.
CN1052688A discloses a fluidized two stages oxidation regeneration process. Spent catalyst is introduced into a first dense bed, contacted with an oxygen-containing gas stream and subjected to a reaction of coke burning. In the first fluidized dense bed, the gas superficial velocity is maintained in the range from 0.8 to 2.5 meter per second, the catalyst average residence time is maintained in the range of 0.6 to 1.0 min, and the regeneration temperature is maintained in the range from 650 to 750° C. A major portion of the carbonaceous deposits are removed by oxidation in the first fluidized bed. Flue gas combined with the partially regenerated catalyst are upwardly introduced to a second fluidized bed via a distributor, and then contacted with an oxygen-containing gas stream to carry out a reaction of coke burning. In second fluidized dense bed the gas superficial velocity is maintained in the range from 1.2 to 3.0 meter per second, the catalyst average residence time is maintained in the range from 1.0 to 2.2 min, and the regeneration temperature is maintained in the range from 700 to 800° C. After being sufficiently regenerated, the regenerated catalyst and flue gas are separated, a part of the regenerated catalyst is reintroduced into the reactor, and the other is introduced into the first fluidized bed.
CN1221022A discloses a residue fluid catalytic cracking process employing an overlapping two-stage regeneration. The first stage regenerator is located on an upper position, in which the regeneration temperature is maintained in the range from 650 to 720° C. The second stage regenerator is located below the first stage regenerator, in which the regeneration temperature is maintained in the range from 650 to 780° C. The two stage regenerators are connected together by a low pressure drop distribution plate and need only one flue gas line and one double slide valve or butterfly valve. Coke contents on the regenerated catalyst are in the range from 0.01 to 0.1% by weight.
Using the high activity zeolite catalyst, the superficial gas velocity in the regenerator is increased to above 0.6 m/s, the coke burning severity is increased to above 100 kg/(h·T), the regeneration temperature is maintained at about 700° C., and the catalyst residence time is reduced to below 4 min. According to the development of regeneration technology, the development direction always focuses on controlling the coke contents on the catalyst to below 0.1% by weight, preferable below 0.05% by weight, and controlling the specific coke burning severity to above 100 kg/(h·T) under a mild deactivating environment and attrition condition, and thereby the activity of the regenerated catalyst can be restored to the highest degree and the maximum conversion of hydrocarbon oils can be obtained.
CN101362959A discloses a catalytic conversion process for propylene and high octane gasoline products. Difficultly cracking oils are contacted with hot regenerated catalyst and subjected to a catalytic cracking reaction under conditions including a reaction temperature between 600° C. and 750° C., a WHSV between 100 h−1 and 800 h−1, a reaction pressure between 0.10 MPa and 1.00 MPa, a catalyst/feedstock oils ratio (C/O) between 30 and 150 by weight and a steam/difficultly cracking oil ratio between 0.05 and 1.0 by weight. The reacted effluents are mixed together with easily cracking oils and subjected to a catalytic cracking reaction under conditions including a reaction temperature between 450° C. and 620° C., a WHSV between 0.1 h−1 and 100 h−1, a reaction pressure between 0.10 MPa and 1.0 MPa, a catalyst/feedstock oil ratio (C/O) between 1.0 and 30 by weight and a steam/difficultly cracking oil ratio between 0.05 and 1.00 by weight. The spent catalyst and product vapors are separated by a cyclone separator. The spent catalyst is then charged into a stripping section and stripped. The stripped spent catalyst is regenerated by burning off the coke and reintroduced into the reactor. The product vapors are separated to obtain desired products comprising propylene, high octane gasoline and recracked oils. Said recracked oils comprise a fraction of distillation range 180 to 260° C. and heavy aromatics extracted oils. The invention greatly improves propylene yield and selectivity, greatly improves gasoline yield and octane number, and decreases the amplitude of dry gas yield by above 80% by weight. Based on a reaction spatio-temporal restraint theory, alkyl-structure groups and aryl-structure groups of the feedstock are separated by a reaction-separation technology. Saturated hydrocarbon in alkyl-structure groups and light aromatics are converted to liquid products by a mild catalytic cracking process. For aryl-structure groups, a part of asphaltenes are adsorbed by the external surface of the catalyst, and polycyclic aromatic hydrocarbons and resins are retained in the upgraded fraction. Thereby an idea of selectively cracking of alkane and alkyl-structure groups is implemented. The fractions which contain more polycyclic aromatic hydrocarbons and resins can be saturated by hydrogen in a hydrogenation unit or extracted in a heavy aromatic extraction unit. The hydrogenated saturated fractions or extracted oils are good quality FCC feedstock which can improve the product selectivity in the FCC and utilize petroleum oil resources efficiently. In order to easily control reaction parameters, it is preferred that the distributions of the catalyst activity and other properties are kept uniform in this process.